Tech Talk #9 – The Big Bang

By David Reher, Reher-Morrison Racing Engines

I haven’t checked the Environmental Protection Agency’s list of endangered species recently, but I’m willing to bet that the small-block V8 is on the list. While the small-block is still the engine of choice in oval track racing and several NHRA sportsman eliminators – notably Stock, Super Stock, Competition, and Pro Stock Truck – the big-block V8 has simply taken over the heads-up eliminators and fast brackets.

There is a reason why the Rat motor reigns as the king of the quarter-mile: the big-block Chevy is durable, heavy-duty, and the best bargain in motor racing.

That’s a total reversal since the days when Buddy Morrison, Lee Shepherd, and I were winning races with small-block Chevys we’d built with junkyard blocks and $25 reground crankshafts. Back then, big-blocks cost big bucks. Today, however, it’s virtually impossible to find a usable 400ci small-block in a salvage yard, and a CNC-machined Bow Tie small-block will set you back $2900. Do the math: You can buy a brand-new Gen VI big-block, an aftermarket forged steel crank, steel H-beam rods, and a set of custom pistons for about the same price – and you’ll end up with a motor with significantly higher performance potential.

Big engines make sense for weekend warriors – the bigger, the better. An engine’s lifespan is directly related to the number of cycles it turns. If you have a large displacement, relatively low-revving engine, it will turn many fewer cycles in a season than a high-revving, small-displacement motor. This means the big engine’s rods will be stretched and its valve springs compressed fewer times. Its roller lifters will make fewer revolutions, and every moving part will be subjected to less stress, wear, and tear.

If you want to race as cheaply as possible and still have a reasonably fast car, my advice is to build or buy a low-rpm, big-inch motor.

You should also have a firm idea of how much horsepower you need to run the number in your particular eliminator. For example, if you need 800 horsepower to make the cut for the Quick 32 at your local track, that’s readily attainable with one of our relatively inexpensive Super 502 engine combinations. If a customer wants a 1200-horsepower engine, I can do that pretty reasonably as well if we make it big – say 588 or 600 cubic inches – and put a nice set of 14-degree Dart Big Chief heads on it. But if someone asks for a real hot rod engine that produces the maximum power for its displacement, then the price tag quickly escalates to Pro Stock levels.

You can compare buying an engine to buying a piece of tubing. If I order a three-foot length of steel tubing with a certain diameter and wall thickness, the clerk at the metal supply can quote me an exact price. But if I want some exotic aerospace material, and I don’t know the length, diameter or thickness, there’s no way the guy behind the counter can give me a price. It’s the same with racing engines: I know what it costs to build a 1,000-horsepower bracket racing big-block because I’ve done it dozens of times – but I have no idea what the price tag would be for a 1,400-horsepower Pro Stock big-block because no one has ever built one.

I’ve noted in previous columns that rpm plays a major role in determining the cost and maintenance requirements of a racing engine. Any engine that regularly turns more than 7,500 rpm really needs lightweight valvetrain components – titanium valves, top-quality rocker arms, serious valve springs. On the other hand, if a 7,000 rpm motor will meet your power requirements, you can build a relatively inexpensive engine that will be virtually bulletproof.

So how big is big enough? I’m sure some engine builders will disagree with me, but I believe the practical limit for a conventional Chevy big-block with 4.840-inch cylinder bore centerlines is 615 cubic inches. I want to emphasis the word “practical.” Back when Buddy, Lee and I raced Mountain Motors, we built 655ci Rat motors with standard blocks, but those were extremely labor intensive. When you consider issues such as camshaft, connecting rod, and oil pan clearance, a 4 5/8-inch stroke crankshaft is about the realistic limit for a standard big-block.

If you want to build a big-block with more than 615 cubic inches, my advice is to go all the way to an aftermarket block with a raised camshaft, spread oil pan rails, and 5.00-inch cylinder bore centerlines. There’s no reason to beat your brains out to get 20 more cubic inches when it’s just as easy (and just as expensive) to build an engine that’s 100 cubic inches bigger. I wouldn’t even consider a block with a 4.900-inch bore centerline like we use in Pro Stock; the little bit you gain with .060-inch more spacing between the cylinders simply isn’t worth the expense for a bracket-type engine.

Aftermarket manufacturers have tooled up to support the new generation of bigger big-blocks with special cylinder heads, oil pans, camshafts, and other specialized components. It’s possible to build a 706ci Rat for Pro Mod or a monster 816ci Mountain Motor – but the price will reflect the cost of the exotic components that are required.

I clearly understand the appeal of big-inch engines for bracket racing and heads-up eliminators. If the rules don’t limit the size of your engine, cubic inches are definitely your friend. They help keep costs down and reliability up. And you can’t have too many friends!